A large number of older car door systems is in use worldwide, in which a crank drive of the door drive in each instance moves at least one car door leaf by way of a drive linkage. In that case usually a crank arm, which can also be present in the form of a crank disc, is so driven by a drive motor in the form of an electric motor via reduction gearing that the crank arm for producing an opening movement or a closing movement of the at least one car door leaf executes a pivot movement of preferably approximately 180°. A crank rod is connected at one end thereof with the end of the crank arm and at the other end thereof with a door drive lever, which is pivotably mounted on a frame of the door drive and coupled at its end with the car door leaf. The components of the described door drive are so shaped and arranged that half a revolution of the crank arm produces a full opening or closing movement of the door leaf, wherein the crank gear ensures an approximately sinusoidal, jolt-free movement of the door leaf with precisely defined end settings. In the case of door systems with more than one car door leaf a second car door leaf can be driven symmetrically with respect to the first car door leaf by the same crank arm via a second crank rod and a second door drive lever.
So that the movement of the car door leaf can be transmitted to the shaft door leaf present at each floor there is usually present at the car door leaf a car door/shaft door coupling which is actuated when the elevator car stops at a floor and which connects the car door leaf with the corresponding shaft door leaf. The car door/shaft door coupling comprises two parallel entrainer skids which are arranged vertically at the car door leaf and which on stopping at a floor come to lie between two counter-bodies—usually in the form of entrainer rollers—present at the shaft door leaf.
The door drive lever is so connected with the car door leaf by way of an adjusting element of the car door/shaft door coupling that at the beginning of the opening movement of the car door leaf the door drive lever imposes on the adjusting element a movement having the consequence of spreading the entrainer skids, whereby a play-free connection between the entrainer skids and the counter-bodies, i.e. a play-free connection between the car door leaf and the shaft door leaf, arises. The door leaves are now synchronously opened and later closed again. At the end of the door closing process the two entrainer skids at the car door leaf are brought into their unspread normal setting by the action of the door drive lever on the said adjusting element, whereby the play-free connection between the car door leaf and the shaft door leaf is cancelled.
Door drives of the described kind have some disadvantages which are briefly explained in the following: The opening and closing movement of the door leaf takes place with an invariable sinusoidal speed course. It is not possible to achieve an optimally small opening and closing time, particularly in the case of wide elevator doors, with such a speed course and with a maximum speed limited for safety reasons. It is also not possible to realize adaptability of the speed course to special situations such as have proved advantageous in the case of, for example, elevators often used by handicapped or elderly passengers. Generation of the door leaf movement by a crank gear additionally has the consequence of a substantial dependence of the closing force on the instantaneous position of the door leaf, i.e. an extremely high closing force can be produced shortly before reaching the closed setting which in the event of failure of a person detection system can lead to situations of being caught. A currently usual method of detecting obstacles by monitoring the motor current or the motor torque at the door drive motor cannot be realized in feasible manner in the case of a door drive with crank gear. The crank gear with reduction gearing and drive linkage moreover forms a source of loud noise which is hardly accepted any longer in current elevator installations. A significant disadvantage is, moreover, to be seen in the fact that the mechanically relatively complex door drive with drive motor, motor brake, crank gear with reduction gearing and several lever joints requires a substantial outlay for checking, maintenance and readjusting and for periodic replacement of the brake linings of the drive motor.
The present invention has the object of proposing measures making it possible to eliminate, with smallest possible cost, the aforesaid disadvantages in existing elevator installations having door leaves moved by a door drive with crank gear and drive linkage. In particular, the measures shall serve for increasing the transport capacity through reducing opening and closing times of the door leaf, reliable avoidance of impermissibly high closing forces, adaptation of the course of the closing speed to special circumstances and minimization of noise output by the door system, wherein the overall cost for such a modernization and also the required conversion time shall be kept as small as possible.